Many products produced by thermoforming, such as plates, bowls, trays, cups, lids, containers, and the like, often require the trimming away of excess material as a final step of the formation process. Various apparatus and methods are known and employed in industry for trimming or severing a plurality of thermoformed articles from a continuous web or sheet of thermoplastic material. Generally, the web of thermoplastic material with the thermoformed articles molded therein is transported from the thermoformer at relatively high rates of speed and throughputs and is then conducted to a trim press for the severing of the thermoformed articles from the web of thermoplastic material. Such trim presses are usually comprised of a stationary platen and a reciprocally movable platen for the mounting of a plurality of cooperating die members, or complementary punch and die members which are conformed to the outer or peripheral configuration of each of the thermoformed articles, and are adapted to provide for concurrent trimming of a number of individual articles from the web.
As thermoforming technology has improved and thermoforming speeds increase, it has become necessary to run trim presses at higher rates of speed in order to continue to provide an in-line trimming operation. A number of patents are directed to improvements in trim press technology for the purpose of increasing the speed of trim press operations. Such patents include U.S. Pat Nos. 4,313,358, 4,391,171, 4,526,074, and 4,890,524, to which reference is made for those details.
While improvements have been made in operations related to the mass production of thermoformed articles, the counting and stacking of those articles is often performed manually. In those operations employing manual stacking, the article, after it is formed and trimmed, may pass into a receptacle or onto a conveyor where it is thereafter manually arranged into a stack. As can be appreciated, this often proves to be quite labor intensive, compared with the rest of the production operation. In such operations, excessive labor costs are often experienced, providing the motivation to automate.
One improved apparatus is described in U.S. Pat. No. 4,526,074, issued to Johnson. U.S. Pat. No. 4,526,074 discloses a system to increase the speed of trim press operations wherein a male locator is adapted to be reciprocated toward and away from a stationary cutter. The locator forces the severed thermoformed article which has been captured by the cutter into a cavity, or die shoe, encompassed by the blade structure. Each subsequent severing operation, wherein a successive thermoformed article is aligned with the cutting blade structure and urged against the cutting edge thereof, upon the forward reciprocating stroke of the male locator, will cause the preceding severed thermoformed article to be forced further into and through the die shoe cavity, thereby producing a stack of trimmed thermoformed articles in a nested relationship which may then be removed for further handling. While U.S. Pat. No. 4,526,074 provides a system which produces a stack of nested articles, the articles must still be removed and counted before packaging for the customer. U.S. Pat. No. 4,526,074 is incorporated by reference for all that it discloses.
A variety of other specialized stackers are known to those skilled in the art. For example, U.S. Pat. No. 3,499,063 discloses an apparatus for collecting and stacking plastic articles received from a blow molding machine. The articles are stacked in a stacking frame which retains the stack by having the lowermost article rest on a spring loaded pawl which extends into the path of incoming articles at the opening. The incoming article moves into the opening, depresses the pawl, moves past the pawl and nests into the stack of articles, lifting the stack from the pawl in the process. Thereafter, the stack of articles is lowered back onto the pawl where it rests until the next article is inserted.
U.S. Pat. No. 4,597,705 relates to an apparatus for the automatic stacking of a predetermined number of pie shells in nested relation for subsequent packaging. The automatic stacking machine disclosed includes an inverted U-shaped structure, the legs of which straddle a conveyor on which the items to be stacked are carried to a location between the legs of the stacker. The legs of the stacker house like means for engaging the item to be stacked on opposite sides and lifting the item to an elevated position where it is deposited on holding means to be retained while the lifting means is returned to the lower position for engaging and lifting the next item to be stacked. When the desired number of items are held in the stack, an automatic kicker means pushes the stacked items off the holding means and onto means for delivering the stack for further processing.
U.S. Pat. No. 4,802,808 discloses a stacking apparatus for deep-drawn plastic articles. The apparatus includes a removal station formed by a support plate forwardly moveable horizontally underneath the raised stack of formed articles, a pushing device arranged above the support plate and moveable parallel relative to the support plate, and a tilting frame located adjacent the support plate when the support plate is in the forwardly moved position.
Although the aforementioned devices have generally performed their intended stacking functions in an acceptable manner, it is to be noted that they do not meet the needs which exist in the mass production of molded articles, such as containers, bowls, plates, trays cups, lids and the like, which require the subsequent trimming or severing of a plurality of the articles from a continuous web or sheet of thermoplastic material. None of the machines known in the art possess the type of utility required by the aforementioned operation.
Therefore what is needed is an apparatus and method for automatically counting and stacking trimmed molded articles which provides the speed and accuracy required in the mass production of such articles.